CVE-2025-5777 is a critical security vulnerability classified as CWE-125 (Out-of-bounds Read) affecting Citrix NetScaler ADC versions 13.1 and 14.1. The vulnerability arises due to insufficient input validation in the NetScaler ADC when it is configured as a Gateway (including VPN virtual server, ICA Proxy, CVPN, RDP Proxy) or as an AAA virtual server. This flaw allows an attacker to trigger a memory overread condition, potentially exposing sensitive information from adjacent memory areas. The vulnerability does not require authentication, user interaction, or privileges to exploit, making it remotely exploitable over the network. The CVSS v4.0 base score is 9.3 (critical), reflecting its high impact on confidentiality, integrity, and availability. The vulnerability could lead to leakage of sensitive data, destabilization of the service, or potentially facilitate further attacks by revealing memory contents that could include credentials or cryptographic material. Although no known exploits are currently reported in the wild, the severity and ease of exploitation make it a significant threat to organizations relying on NetScaler ADC for secure remote access and authentication services.

For European organizations, the impact of CVE-2025-5777 is substantial due to the widespread use of Citrix NetScaler ADC in enterprise environments for secure remote access, VPN services, and authentication. Exploitation could lead to unauthorized disclosure of sensitive corporate data, including user credentials and session tokens, undermining confidentiality. The integrity of authentication processes could be compromised, allowing attackers to bypass security controls or escalate privileges. Availability may also be affected if the memory overread leads to crashes or service disruptions, impacting business continuity. Given the critical role of NetScaler ADC in securing remote workforces and cloud access, exploitation could facilitate lateral movement within networks, data exfiltration, or disruption of critical services. This is particularly concerning for sectors with stringent data protection requirements under GDPR, such as finance, healthcare, and government agencies across Europe.

To mitigate CVE-2025-5777, European organizations should prioritize the following actions: 1) Immediately verify if their NetScaler ADC deployments are running affected versions 13.1 or 14.1, especially those configured as Gateway or AAA virtual servers. 2) Apply vendor-provided patches or updates as soon as they become available; if no patches are currently released, engage with Citrix support for interim mitigation guidance. 3) Implement network-level protections such as restricting access to NetScaler ADC management and gateway interfaces to trusted IP ranges and deploying Web Application Firewalls (WAF) or Intrusion Prevention Systems (IPS) with signatures tuned to detect anomalous traffic patterns targeting this vulnerability. 4) Monitor logs and network traffic for unusual activity indicative of exploitation attempts, including unexpected memory access errors or crashes. 5) Employ strict segmentation and least privilege principles to limit the potential impact of a compromised NetScaler ADC instance. 6) Conduct regular vulnerability scanning and penetration testing focused on remote access infrastructure to detect similar issues proactively.